From 9edccd3ba669951b064ba0c6f46a62dd93f5e3f9 Mon Sep 17 00:00:00 2001 From: Imran Zaheer Date: Thu, 4 Jun 2026 17:08:27 +0500 Subject: [PATCH v1] Move system identifier generation to a common helper The code used to generate a new system identifier is duplicated in multiple locations, including BootStrapXLOG(), pg_createsubscriber and pg_resetwal. Move the implementation to a common GenerateSystemIdentifier() helper and update existing callers to use it. This allows both backend and frontend code to share a single implementation of the system identifier generation algorithm. --- src/backend/access/transam/xlog.c | 20 +------- src/bin/pg_basebackup/pg_createsubscriber.c | 9 +--- src/bin/pg_resetwal/pg_resetwal.c | 14 ++---- src/common/Makefile | 1 + src/common/meson.build | 1 + src/common/system_identifier.c | 56 +++++++++++++++++++++ src/include/common/system_identifier.h | 19 +++++++ 7 files changed, 84 insertions(+), 36 deletions(-) create mode 100644 src/common/system_identifier.c create mode 100644 src/include/common/system_identifier.h diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index d69d03b2ef3..0d2a49172e4 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -43,7 +43,6 @@ #include #include #include -#include #include #include "access/clog.h" @@ -69,6 +68,7 @@ #include "catalog/pg_database.h" #include "common/controldata_utils.h" #include "common/file_utils.h" +#include "common/system_identifier.h" #include "executor/instrument.h" #include "miscadmin.h" #include "pg_trace.h" @@ -5460,28 +5460,12 @@ BootStrapXLOG(uint32 data_checksum_version) XLogRecord *record; char *recptr; uint64 sysidentifier; - struct timeval tv; pg_crc32c crc; /* allow ordinary WAL segment creation, like StartupXLOG() would */ SetInstallXLogFileSegmentActive(); - /* - * Select a hopefully-unique system identifier code for this installation. - * We use the result of gettimeofday(), including the fractional seconds - * field, as being about as unique as we can easily get. (Think not to - * use random(), since it hasn't been seeded and there's no portable way - * to seed it other than the system clock value...) The upper half of the - * uint64 value is just the tv_sec part, while the lower half contains the - * tv_usec part (which must fit in 20 bits), plus 12 bits from our current - * PID for a little extra uniqueness. A person knowing this encoding can - * determine the initialization time of the installation, which could - * perhaps be useful sometimes. - */ - gettimeofday(&tv, NULL); - sysidentifier = ((uint64) tv.tv_sec) << 32; - sysidentifier |= ((uint64) tv.tv_usec) << 12; - sysidentifier |= getpid() & 0xFFF; + sysidentifier = GenerateSystemIdentifier(); memset(&buffer, 0, sizeof buffer); page = (XLogPageHeader) &buffer; diff --git a/src/bin/pg_basebackup/pg_createsubscriber.c b/src/bin/pg_basebackup/pg_createsubscriber.c index cb16a608002..2869057e013 100644 --- a/src/bin/pg_basebackup/pg_createsubscriber.c +++ b/src/bin/pg_basebackup/pg_createsubscriber.c @@ -25,6 +25,7 @@ #include "common/logging.h" #include "common/pg_prng.h" #include "common/restricted_token.h" +#include "common/system_identifier.h" #include "datatype/timestamp.h" #include "fe_utils/recovery_gen.h" #include "fe_utils/simple_list.h" @@ -709,7 +710,6 @@ modify_subscriber_sysid(const struct CreateSubscriberOptions *opt) { ControlFileData *cf; bool crc_ok; - struct timeval tv; char *out_file; char *cmd_str; @@ -722,13 +722,8 @@ modify_subscriber_sysid(const struct CreateSubscriberOptions *opt) /* * Select a new system identifier. - * - * XXX this code was extracted from BootStrapXLOG(). */ - gettimeofday(&tv, NULL); - cf->system_identifier = ((uint64) tv.tv_sec) << 32; - cf->system_identifier |= ((uint64) tv.tv_usec) << 12; - cf->system_identifier |= getpid() & 0xFFF; + cf->system_identifier = GenerateSystemIdentifier(); if (dry_run) pg_log_info("dry-run: would set system identifier to %" PRIu64 " on subscriber", diff --git a/src/bin/pg_resetwal/pg_resetwal.c b/src/bin/pg_resetwal/pg_resetwal.c index f8d25afed9d..c5a755e4ea9 100644 --- a/src/bin/pg_resetwal/pg_resetwal.c +++ b/src/bin/pg_resetwal/pg_resetwal.c @@ -39,7 +39,6 @@ #include #include #include -#include #include #include @@ -54,6 +53,7 @@ #include "common/logging.h" #include "common/restricted_token.h" #include "common/string.h" +#include "common/system_identifier.h" #include "fe_utils/option_utils.h" #include "fe_utils/version.h" #include "getopt_long.h" @@ -669,9 +669,6 @@ read_controlfile(void) static void GuessControlValues(void) { - uint64 sysidentifier; - struct timeval tv; - /* * Set up a completely default set of pg_control values. */ @@ -683,14 +680,9 @@ GuessControlValues(void) /* * Create a new unique installation identifier, since we can no longer use - * any old XLOG records. See notes in xlog.c about the algorithm. + * any old XLOG records. */ - gettimeofday(&tv, NULL); - sysidentifier = ((uint64) tv.tv_sec) << 32; - sysidentifier |= ((uint64) tv.tv_usec) << 12; - sysidentifier |= getpid() & 0xFFF; - - ControlFile.system_identifier = sysidentifier; + ControlFile.system_identifier = GenerateSystemIdentifier(); ControlFile.checkPointCopy.redo = SizeOfXLogLongPHD; ControlFile.checkPointCopy.ThisTimeLineID = 1; diff --git a/src/common/Makefile b/src/common/Makefile index 1a2fbbe887f..4299090c107 100644 --- a/src/common/Makefile +++ b/src/common/Makefile @@ -77,6 +77,7 @@ OBJS_COMMON = \ rmtree.o \ saslprep.o \ scram-common.o \ + system_identifier.o \ string.o \ stringinfo.o \ unicode_case.o \ diff --git a/src/common/meson.build b/src/common/meson.build index 9bd55cda95b..65cf160f144 100644 --- a/src/common/meson.build +++ b/src/common/meson.build @@ -31,6 +31,7 @@ common_sources = files( 'rmtree.c', 'saslprep.c', 'scram-common.c', + 'system_identifier.c', 'string.c', 'stringinfo.c', 'unicode_case.c', diff --git a/src/common/system_identifier.c b/src/common/system_identifier.c new file mode 100644 index 00000000000..acb07f3834c --- /dev/null +++ b/src/common/system_identifier.c @@ -0,0 +1,56 @@ +/*------------------------------------------------------------------------- + * + * system_identifier.c + * Implementation of system identifier generation + * + * Portions Copyright (c) 2026, PostgreSQL Global Development Group + * + * + * IDENTIFICATION + * src/common/system_identifier.c + * + *------------------------------------------------------------------------- + */ +#ifndef FRONTEND +#include "postgres.h" +#else +#include "postgres_fe.h" +#endif + +#include +#include + +#include "common/system_identifier.h" + +/* + * GenerateSystemIdentifier + * + * Creates a reasonably unique 64-bit identifier using: + * - current time (seconds + microseconds) + * - process ID + */ +uint64 +GenerateSystemIdentifier(void) +{ + struct timeval tv; + uint64 sysidentifier; + + /* + * Select a hopefully-unique system identifier code for this installation. + * We use the result of gettimeofday(), including the fractional seconds + * field, as being about as unique as we can easily get. (Think not to + * use random(), since it hasn't been seeded and there's no portable way + * to seed it other than the system clock value...) The upper half of the + * uint64 value is just the tv_sec part, while the lower half contains the + * tv_usec part (which must fit in 20 bits), plus 12 bits from our current + * PID for a little extra uniqueness. A person knowing this encoding can + * determine the initialization time of the installation, which could + * perhaps be useful sometimes. + */ + gettimeofday(&tv, NULL); + sysidentifier = ((uint64) tv.tv_sec) << 32; + sysidentifier |= ((uint64) tv.tv_usec) << 12; + sysidentifier |= getpid() & 0xFFF; + + return sysidentifier; +} \ No newline at end of file diff --git a/src/include/common/system_identifier.h b/src/include/common/system_identifier.h new file mode 100644 index 00000000000..5ef7600c80d --- /dev/null +++ b/src/include/common/system_identifier.h @@ -0,0 +1,19 @@ +/*------------------------------------------------------------------------- + * + * system_identifier.h + * Common utility to generate a system identifier + * + *------------------------------------------------------------------------- + */ + +#ifndef SYSTEM_IDENTIFIER_H +#define SYSTEM_IDENTIFIER_H + +#include + +/* + * Generate a new system identifier. + */ +extern uint64 GenerateSystemIdentifier(void); + +#endif /* SYSTEM_IDENTIFIER_H */ \ No newline at end of file -- 2.34.1